One of the physical signs of circulatory shock is the loss of warmth in the hands and feet. This results from an inadequacy of blood flow in the extremities. Accordingly, it has been recognized that peripheral skin temperature can provide an indication of blood flow. Studies conducted by the applicant have shown that the peripheral skin temperature, and more particularly the skin temperature taken at a toe of a patient, can provide a good indication of the cardiac output of the patient, and provide a good indication of the likelihood of survival of a critically ill patient suffering from circulatory shock. Furthermore, these studies have shown that a somewhat better accuracy of indication can be obtained by measuring the difference between the toe temperature of the patient and the ambient air temperature. Knowledge about the likelihood of survival of a critically ill patient undergoing circulatory shock, at a time considerably before the appearance of other symptoms indicating this can be useful in determining the treatment to be administered and in assessing the effect of such treatment. A method and apparatus that provided an even more accurate indication of the patient's condition, in a manner that was easily performed and with minimal trauma to the patient, would be of considerable value.